Plasmamembrane ghosts have been prepared from axenically grown amoebae of Dictyostelium discoideum by stabilizing the membrane with purified lectin and lysing the cell with Triton X-100. The stable membrane ghosts retain certain distinctive plasmamembrane enzyme markers and do not appear to be contaminated with nucleic acid or cytoplasmic components. Regions of membrane with capped lectin can also be prepared by the same procedure resulting in the isolation of caps. In the proposed study, ghosts and isolated caps will be purified and used as model membranes to study the ultrastructure and biochemistry of the actin cytoskeleton that is associated with plasmamembrane containing lectin receptors. Peripheral proteins will be extracted from the membranes using mild aequeous buffers. These proteins will be purified and characterized and their properties compared to proteins composing motile cytoplasmic extracts prepared from Dicytostelium amoebae. Mild extraction with aqueous buffers will remove peripheral proteins while integral components remain associated with the membrane. Inside out and right side out sealed vesicles will be prepared from the extracted membranes and used to study the primary actin binding site on the membrane by a detailed binding study using radiolabelled actin. Nearest neighbor analysis using bifunctional reagents will be used to identify components on the vesicle membrane to which actin binds.